This invention relates to the field of heat exchangers in which heat is taken up by a series of coils from a heat source and transferred to air flowing in a hot air duct of a hot air heating system.
One of the major problems regarding heat exchangers which are presently known is relatively low efficiency. That is, the amount of heat actually transferred to the air being heated is a relatively low percentage of that actually available at the heat source. The present invention makes a marked improvement in efficiency and percentage of heat available at the source that is actually transferred to the air in an air duct which is to be heated.
Examples of prior art heat exchangers of which the inventor is aware include the one disclosed in U.S. Pat. No. 4,261,326, comprising a coil in which gases are drawn by a blower positioned to create negative atmospheric pressure at the exhaust end. U.S. Pat. No. 2,528,623 discloses another type of heating coil in which low pressure is induced at the exhaust end. U.S. Pat. No. 2,155,184 discloses an orchard heater having a series of laterally extending pipes through which the steam is flowed by a blower. U.S. Pat. No. 1,516,458 discloses a heating coil assembly through which hot gases are flowed with a blower creating the draft necessary to move the gases through the coils.
The present invention improves efficiency of the heat exchanger by providing a vacuum or "pulling force" which is downstream of the heat transfer coils, the vacuum being created by flowing outside relatively colder air in a stack transversely of the opening to the passageway from which the relatively hotter air is being drawn past the heat transfer coils. The relatively colder and heavier air in the transversely positioned stack tends to impede the entry of relatively hotter and lighter air into the transverse stack until its temperature has been significantly reduced. This enables the heated air from the burner and heating chamber to more or less flow through the heat transfer coils at its own pace allowing maximum take up and transfer of heat, until the temperature of the heated air is significantly lowered toward that of the outside air being flowed through the transverse stack. There is no "pushing force" upstream of the heat transfer coils, nor even any positive force of either the pushing or pulling variety in the hot air passageway of this invention that positively propels the hot air along at a constant rate as it passes through the heat transfer coils, forcing it to continue at that constant flow rate whether it has given up all of its heat to the heat transfer coils or not.